1. Field of the Invention
The present invention relates to communication networks. More specifically, the present invention relates to a method and an apparatus for providing a guaranteed level of availability in a communication network.
2. Related Art
Network communication technologies provide for a wide range of interconnections and bandwidths. For example, wavelength-division multiplexing (WDM) technology enables a single optical fiber to support over one hundred wavelength channels, each of which can operate at a bandwidth of several gigabits per second (Gbps). Providing this amount of capacity through a single optical fiber has significant advantages, such as greatly reduced cost. However, a failure in such an optical network, e.g., a fiber cut or fiber conduit cut, can lead to the loss of a huge amount of data (several terabits per second (Tbps) to several petabits per second (Pbps)), and can result in penalties under a service level agreement.
When a connection through the WDM network is requested, a service provider and a client typically enter into a service level agreement (SLA), which provides a specified service level to the client, and provides penalties on the provider if the service level is not met. The service provider receives compensation based, inter alia, upon the service level requested and the level of penalties specified in the SLA. Upon acceptance of the SLA by both provider and client, the circuit is provisioned.
In the traditional connection-provisioning scheme, a shortest path (based on the link cost) between the source node and the destination node is chosen to route a given connection request. Depending on different traffic-engineering considerations, different cost functions can be applied to network links, such as a constant 1 for each link (to minimize hop distance), the length of the link (to minimize delay), the fraction of the available capacity on the link (to balance network load), etc. However, this traditional connection-provisioning scheme is unaware of any connection-availability requirements. Consequently, the route computed by a shortest-path algorithm may not satisfy the SLA, because the route may not be reliable enough.
FIG. 1 illustrates a shortest path through a WDM network, which does not meet the availability requirement of an SLA. A connection request is made from node 0 to node 5 and this request specifies an availability requirement of 95%. In FIG. 1, the integers next to the links represent the link costs. In this example, the route (0, 3, 4, 5), route 1, is indicated by the dashed lines and is the least-cost path (cost=3).
Unfortunately, this least-cost path does not consider connection availability requirements. Referring to FIG. 1, the percentages next to the links represent the estimated availability of each link. Note that each of the links has an availability of 99%, except for the link between nodes 4 and 5, which has an availability of 90%. This low availability can be the result of a number of factors, such as old fibers, fibers routed through areas of heavy construction, etc. The estimated availability of route 1 is the product of the availabilities of the links that the connection traverses. For route 1, the availability is 88.21%, which is less than the required availability in the SLA.
Hence, what is needed is a method and an apparatus for providing a guaranteed level of availability in a communication network.